A. Hong1,2, D. Bolton1,3, S. Ramani4, J. Ischia1, D. Lim Joon5, F. Foroudi6, G. Jack1, and M. Chao2,6; 1Austin Health, Melbourne, VIC, Australia, 2University of Melbourne, Melbourne, VIC, Australia, 3Olivia Newton John Cancer Centre, Melbourne, Australia, 4Southport, Brisbane, QLD, Australia, 5Olivia Newton John Cancer Centre, Melbourne, VIC, Australia, 6Olivia Newton John Cancer Wellness and Research Centre, Austin Hospital, Melbourne, VIC, Australia
Purpose/Objective(s): Radiation therapy for prostate cancer may cause gastrointestinal (GI) toxicity as the rectum is an organ at risk. Stabilized hyaluronic acid (sHA) has recently been approved for use as a rectal spacer and reduces GI toxicity in this setting. It has several advantages, including its reversibility using hyaluronidase. This is particularly beneficial in cases of rectal wall infiltration (RWI). The use of non-reversible rectal spacers may lead to severe adverse outcomes such as mucosal ulceration, pelvic abscess and recto-prostatic fistula after RWI. As such, we aim to assess the outcomes of inadvertent RWI by sHA rectal spacers. Materials/
Methods: A retrospective analysis of patients who had inadvertent RWI following the use of sHA rectal spacers was conducted in Australia. More than 5000 patients have had sHA rectal spacing with the majority undergoing magnetic resonance imaging (MRI) simulation. Patients with RWI were identified based on post-procedural MRI. Data collection included patient demographics, delays in radiation therapy, grade of the RWI and symptoms, and management of the RWI. The patients were followed up during and post radiation therapy and assessed for rectal complications. Results: A total of 16 prostate cancer patients were identified to have RWI after sHA spacer insertion. The grade of RWI as defined by Fischer Valuck criteria were as follows: Grade 1, N=5; Grade 2, N=6; and Grade 3, N=5. The median volume of misplaced sHA was 2.8 cc from an average total of 9cc used. No post procedural GI symptoms were reported. A sigmoidoscopy was performed in 12 patients including all 5 with grade 3 RWI, and all of these showed intact rectal mucosa. Seven patients underwent targeted reversal procedures while 9 patients were monitored. Of those who underwent reversal procedures, the median (and mean) volume of misplaced hyaluronic acid is 4 mL (3.8mL), compared to 1.5 mL (2.1mL) in those who did not undergo reversal (Mann-Whitney U test, p=0.1). All 7 who underwent reversal with hyaluronidase were successful. No post reversal complications were reported. One patient underwent successful reinsertion of sHA following reversal. Initiation of radiation therapy was delayed in 11 cases by a median of 3.2 months. All patients completed their RT as planned. No acute grade 2 or higher GI toxicity was reported in any of the 16 patients. Conclusion: This case series presents the first evidence for the safety of sHA rectal spacer in cases of RWI, with an event rate of less than 0.03% We have proven the efficacy of hyaluronidase in reversal of RWI with HA with the majority of patients experiencing minimal delay in commencement of RT. No severe adverse complications were reported.
